Turn off auto_calculate_length_and_angle on leaf bones

Fix warnings "WARNING: No Bone2D children of node Chin. Cannot calculate
bone length or angle reliably. Using transform rotation for bone angle."

Those warnings were output for each Bone2D without any child Bone2D:
* Chin
* LeftFoot
* LeftHand
* RightFoot
* RightHand

Disabling the auto calculation seems to have filled in lengths and
bone_angles. Presumably these are the transform rotations that it would
use anyway.

Test
* run and jump around the world and animations look correct to me.

2d/skeleton/player/player.tscn

@@ -1811,6 +1811,9 @@ rest = Transform2D(1, 0, 0, 1, 0, -160)
 position = Vector2(0, -49)
 rotation = -0.0435718
 rest = Transform2D(0.999999, 0.00169551, -0.00169551, 0.999999, 0, -49)
+auto_calculate_length_and_angle = false
+length = 16.0
+bone_angle = -2.49648
 
 [node name="RightArm" type="Bone2D" parent="Sprite2D/Skeleton2D/Hip/Chest"]
 position = Vector2(80, -100)
@@ -1826,6 +1829,9 @@ rest = Transform2D(1, 0, 0, 1, -11, 97)
 position = Vector2(13, 94)
 rotation = 1.22745
 rest = Transform2D(0.336639, 0.941634, -0.941634, 0.336639, 13, 94)
+auto_calculate_length_and_angle = false
+length = 16.0
+bone_angle = 70.3277
 
 [node name="LeftArm" type="Bone2D" parent="Sprite2D/Skeleton2D/Hip/Chest"]
 position = Vector2(-100, -100)
@@ -1841,6 +1847,9 @@ rest = Transform2D(1, 0, 0, 1, -2, 95)
 position = Vector2(9, 102)
 rotation = 1.22983
 rest = Transform2D(0.334394, 0.942433, -0.942433, 0.334394, 9, 102)
+auto_calculate_length_and_angle = false
+length = 16.0
+bone_angle = 70.4641
 
 [node name="LeftLeg" type="Bone2D" parent="Sprite2D/Skeleton2D/Hip"]
 position = Vector2(-72, 26)
@@ -1855,6 +1864,9 @@ rest = Transform2D(1, 0, 0, 1, -13, 91)
 [node name="LeftFoot" type="Bone2D" parent="Sprite2D/Skeleton2D/Hip/LeftLeg/LeftLowerLeg"]
 position = Vector2(7, 127)
 rest = Transform2D(1, 0, 0, 1, 7, 127)
+auto_calculate_length_and_angle = false
+length = 16.0
+bone_angle = 0.0
 
 [node name="RightLeg" type="Bone2D" parent="Sprite2D/Skeleton2D/Hip"]
 position = Vector2(46, 11)
@@ -1870,6 +1882,9 @@ rest = Transform2D(1, 0, 0, 1, -26, 94)
 [node name="RightFoot" type="Bone2D" parent="Sprite2D/Skeleton2D/Hip/RightLeg/RightLowerLeg"]
 position = Vector2(2, 129)
 rest = Transform2D(1, 0, 0, 1, 2, 129)
+auto_calculate_length_and_angle = false
+length = 16.0
+bone_angle = 0.0
 
 [node name="Polygons" type="Node2D" parent="Sprite2D"]